A book review usually appears in a magazine or journal soon after the publication of a book; reprints, later editions and reissues are often not reivewed, so it's important to have the original publication date. For electronic sources, a keyword search on a word from the title or author’s name (plus the word review) is often sufficient.
Note for literature students: while reviewers are referred to as critics, reviews have a different purpose from literary criticism. Ask a reference librarian for good sources of literary criticism, as well as for reviews.
To limit retrieved reviews from databases to scholarly reviews only, be sure to select the Peer Reviewed or Scholarly Journals limiter in the database you are searching.
Some databases, such as JSTOR and Project Muse, will allow you to limit to Reviews. For those that don't, including "book reviews" as a search term will help to narrow your search to reviews only.